Enhanced oil recovery method employing an aqueous polymer

ABSTRACT

A stable latex composition possessing a viscosity of less than about 50 cp. comprised of an ethylacrylate/methylacrylic acid/acrylic acid polymer and co-surfactant system comprising a nonylphenol polyethylene oxide ether sulfate and a propoxylated, ethoxylated propylene glycol nonionic surfactant block polymer useful for increasing the viscosity of water that is injected into subterranean petroleum bearing formations for the enchanced recovery of the petroleum.

This application is a division of application Ser. No. 751,570, filedJune 27, 1985, now U.S. Pat. No. 4,753,973 which is acontinuation-in-part of U.S. patent application Ser. No. 673,421, filedNov. 20, 1984, allowed U.S. Pat. No. 4,808,648.

BACKGROUND OF INVENTION

The present invention relates to a stable latex useful for increasingthe viscosity of water and for the enhanced recovery of subterraneanoil.

Enhanced oil recovery is typically carried out by flushing theoil-containing subterranean formations with a fluid capable ofdisplacing the oil in the formation. This fluid is injected into theformation through at least one injection well so as to drive the oilthrough the formation to at least one production well. Fluids useful forenhanced oil recovery may either be a liquid or a gas with the mosteconomical and widely used fluid being water. The major drawback withwater is that it does not displace the petroleum efficiently since it isnot immiscible with oil and because the interfacial tension between oiland water is quite high. The result is that the water will generallymove past the oil to a more permeable are of the formation leavingbehind substantial quantities of residue oil in the oil-bearingformations.

Various means have been developed to reduce the interfacial tensionbetween the water and oil. This generally involves admixing varioustypes of surfactants with water.

Typical surfactants, which have been used to reduce the interfacialtension between the water and the oil in subterranean formations, arethe various types of sulfates and sulfonates, such as petroleum sulfatesand sulfonates.

It is also generally desirable to provide the water with a viscositygreater than that of the oil present in the subterranean formation toincrease the effectiveness of water in displacing the oil. The viscosityof the water may be increased by preparing aqueous emulsions ordispersions having a dispersed hydrocarbon phase, by dispersing ahydrocarbon, for example crude oil or distilled fractions of crude oilinto water using surfactants such as the sulfonates or sulfates.

It is also known that the viscosity of water may be increased bypreparing aqueous solutions or emulsions of certain types of polymers.Typically, a concentrated composition of these polymers is preparedwhich can be blended with water at the well site to increase theviscosity of the water prior to injection into the subterraneanformation. U.S. Pat. No. 3,909,423 discloses a composition ofpolyacrylamides, polymethacrylamides, and water wherein a portion of thecarboxyamide group has been hydrolyzed to form carboxyl groups which canthen be cross linked so as to increase the viscosity of the water.

U.S. Pat. No. 3,891,567 discloses aqueous compositions which containfrom about 0.001 percent to about 10 percent of a particularlyhydrolyzed polyacrylamide and about 0.001 percent to about 10 percent ofa carboxyl vinyl polymer. These compositions are disclosed as a floodingmedium for recovering oil from subterranean oil-bearing formations.

U.S. Pat. No. 3,679,000 discloses a process for tertiary oil recoverywhich comprises injecting viscous water into the area of the oil depositthrough an input well by incorporating into the water a minor amount ofa water soluble polymer containing 5 percent of a repeating unit of theformula: ##STR1## wherein R₁ is a hydrogen or lower alkyl,

R₂ is a divalent or trivalent hydrocarbon,

M is hydrogen or one equivalent of a cation, and

X is one or two.

U.S. Pat. No. 4,148,746 discloses aqueous gels suitable as waterthickening agents and are useful for enhanced oil recovery. This waterthickening gel is prepared by polymerizing at least one alkyl acrylatemonomer and at least one carboxylic polymerizable monomer selected fromthe group consisting of acrylic acid and methylacrylic acid. Thecarboxylic polymerizable monomer is present from 20 to 95 parts perweight per 100 parts of total monomer being polymerized and utilizing.The composition is disclosed as comprised of an emulsifier selected fromthe group consisting of disodium or diammonium nonylphenoxy polyethoxysulfosuccinate having the general formula:

    CH.sub.3 (CH.sub.2).sub.8 C.sub.6 H.sub.4 O(CH.sub.2 CH.sub.2 O).sub.8-16 COCH.sub.2 CH(COOM)SO.sub.3 Q

wherein Q is sodium or ammonium and a sodium or ammonium laurylpolyethoxysulfate having the general formula:

    CH.sub.2 (CH.sub.2).sub.11 O(CH.sub.2 CH.sub.2 O).sub.8-16 SO.sub.3 Q

wherein Q is sodium or ammonium, the polymer is in a latex form which isneutralized to a pH ranging between a pH of 5.5 to 11.5. These polymersalso may be gelled with a water soluble polyvalent compound such assodium dichromate and a water soluble reducing agent such as sodiumhydrosulfite.

It should be evident that there are numerous types of polymers usefulfor increasing the viscosity of water. Since water is the cheapest fluidfor enhanced oil recovery, it is desirable to produce an aqueouscomposition containing the lowest cost polymers for enhanced oilrecovery operations. Some of the previously known polymers such as thosecomprising acrylamide, can significantly increase the cost of aqueouscompositions compared to other types of polymer systems.

Besides low cost polymers the cost of using polymers for increasing theviscosity of water may be reduced by preparing aqueous polymericcompositions, such as latexes, with a high solids percentage of thepolymer in the composition. These concentrated polymer compositions aretypically transported to the well site and admixed with water, with themixture injected into the formation. A high solids-containing emulsionor latex reduces the cost of operation because of the reduced cost oftransporting the composition to the well site. Aqueous polymercompositions, such as those disclosed in U.S. Pat. No. 4,148,746,typically have solid contents around 20 percent.

It should be noted that, while it is desirable to increase the weightpercent of polymer in the composition the stability of the compositionduring preparation, storage, transportation, and/or use in enhanced oilrecovery should be such that the polymer does not precipitate out ofsolution and thus create the potential for plugging the subterraneanformation.

It can thus be seen that it would be desirable to provide a stableaqueous composition containing a high percent solids level of aninexpensive polymer capable of increasing the viscosity of water usedfor enhanced oil recovery.

SUMMARY OF THE PRESENT INVENTION

In one embodiment the present invention resides in a stable latexcomposition comprising:

water;

at least one polymer comprising from about 45 to about 65 weight percentethylacrylate monomer residue, from about 10 to about 45 weight percentmethylacrylic acid monomer residue and from about 20 to about 30 weightpercent acrylic acid monomer residue;

at least one nonylphenol polyethylene oxide ether sulfate, wherein thepolyethylene oxide adduct of the nonylphenol polyethylene oxide ethersulfate is comprised of at least about 20 moles of ethylene oxidemonomer residue; and

wherein the polymer and the nonylphenol polyethylene oxide ether sulfateare present in an amount sufficient to provide the stable latexcomposition with a viscosity of less than about 50 centipoise.

In another embodiment of the present invention at least onepropoxylated, ethoxylated propylene glycol nonionic surfactant blockpolymer is used as a co-surfactant with the nonylphenol polyethyleneoxide ether sulfate.

The present invention also relates to solutions prepared from thiscomposition and a method of using this latex composition in the recoveryof subterranean oil.

DETAILED DESCRIPTION OF THE INVENTION

The stable latex composition of the present invention is an emulsionprepared by the emulsion polymerization of ethylacrylate, acrylic acid,and methylacrylic acid monomers by any of the known emulsionpolymerization techniques. Preferably, the polymerization is by a freeradical polymerization technique. It has unexpectedly been found thatthis latex composition can be prepared having a high polymer solidscontent while having a low viscosity and remaining stable duringpreparation and storage and yet be useful for preparing a high viscosityaqueous solution useful as an enhanced oil recovery fluid.

As stated, it has unexpectedly been found that the latex composition ofthe present invention can be prepared having a high weight percentage ofpolymer with a low viscosity. This is the result of not only using theparticular types and amounts of monomers in preparing the polymer but bythe use of a particular type of surfactant which not only assists in theemulsion polymerization of the monomers but also assists in providingthe stability of the composition. In one embodiment the particularsurfactant useful for the purposes of the present invention isnonylphenol polyethylene oxide ether sulfate wherein the polyethyleneoxide adduct of the ether sulfate is comprised of at least about 20moles of ethylene oxide monomer residue and preferably from about 20 toabout 30 moles. The nonylphenol polyethylene oxide ether sulfate of thepresent invention has the following general formula: ##STR2## wherein nis at least about 20, preferably from about 20 to about 30, and

X is any suitable cation.

By moles of ethylene oxide monomer residue present in the adduct, it ismeant the number average of moles for a given mixture of nonylphenolpolyethylene oxide ether sulfate. Suitable cations are sodium,potassium, ammonium, and preferably sodium.

In another embodiment, a co-surfactant system is used comprising atleast one nonylphenol polyethylene oxide ether sulfate and at least onepropoxylated, ethoxylated propylene glycol nonionic surfactant blockpolymer of the general formula:

    HO(CH.sub.2 CH.sub.2 O).sub.a [CH(CH.sub.3)CH.sub.2 O].sub.b (CH.sub.2 CH.sub.2 O).sub.c H

wherein a, b and c are positive integers and wherein a and c total fromabout 10 to about 100, e.g. from about 30 to about 50 and b ranges fromabout 5 to about 50. This type of surfactant comprises block polymers ofethylene oxide and propylene oxide, with the repeating units ofpropylene oxide constituting the hydrophobic portion of the surfactantand the repeating units of ethylene oxide constituting the hydrophilicportion of the surfactant. These type of surfactants can be prepared,and are commercially available, in a variety of molecular weights,depending primarily on the number of repeating units of propylene andethylene oxide.

Suitable procedures for the production of these block polymers of theabove formula are described in the patent literature in, for example,U.S. Pat. Nos. 2,674,619; 2,677,700 and 3,101,374, all three of whichare incorporated herein by reference. Generally, these block polymersare prepared by a controlled addition of propylene oxide to the twohydroxyl groups of propylene glycol to form the hydrophobe, followed bythe controlled addition of ethylene oxide to "sandwich" in thehydrophobe between the two hydrophilic polyethyleneoxide groups. Thesenonionic surfactants are available from the BASF-Wyandotte Corporationunder the Pluronic designation.

As already stated, the latex composition of the present invention isstable; that means it remains homogeneous without any precipitateformation even at a high weight percentage of polymer when the pH of thecomposition is from about 2 to about 4 and at temperatures of about 32°F. to about 120° F. The amount of surfactant and polymer comprising thelatex composition of the present invention is dependent upon theviscosity desired in the end use. Preferably, the composition iscomprised of an amount of polymer and surfactant sufficient to provide astable latex having a viscosity of less than about 50 centipoise (cp)more preferably from about 5 cp to about 20 cp, as measured using aBrookfield Synchro-Lectric viscometer equipped with a number 1 spindlerevolving at 30 revolutions per minute (rpm) at room temperature (about70° F.).

Preferably, the composition of the present invention comprises at leastabout 5 weight percent solids of the polymer, more preferably, at leastabout 21 weight percent, and still more preferably from about 21 toabout 30 weight percent solids.

Generally, the polymer of the latex composition of the present inventionis comprised of about 45 to about 65 weight percent ethylacrylatemonomer residue, from about 20 to about 30 weight percent acrylic acidmonomer residue and from about 10 to about 45 weight percentmethylacrylic acid monomer residue. As the weight percent solids of thepolymer in the latex composition increases, the weight percent of theparticular monomers making up the polymer are adjusted to provide thecomposition with a viscosity of less than about 50 centipoise,preferably from about 5 to about 20 cp as discussed above. Preferably,when the weight percent solids content of the polymer is from about 21to about 30, the polymer is comprised of about 55 to about 65 weightpercent ethylacrylate monomer residue, from about 10 to about 25 weightpercent acrylic acid monomer residue and from about 10 to about 30weight percent methylacrylic acid monomer residue, and when the weightpercent solids content of the polymer is from about 30 to about 35, thepolymer is comprised from about 60 to about 65 weight percentethylacrylate monomer residue, from about 10 to about 15 weight percentacrylic acid monomer residue and from about 20 to about 30 weightpercent methylacrylic acid monomer residue. All reference herein toweight percent with respect to the monomers is based upon the totalweight percent monomers used in preparing the polymer of the presentinvention.

In accordance with one embodiment the preferred amount of thenonylphenol polyethylene oxide ether sulfate useful for providing thecomposition of the present invention with a viscosity of less than about50 centipoise at about 70° F. is from about 2 to about 10 parts per 100parts of the monomer being polymerized, and more preferably from about 2to about 4 parts per 100 parts of the monomer being polymerized.

In accordance with the co-surfactant system embodiment the totalcombined amount of the co-surfactant is from about 2 to about 10, morepreferably about 2 to about 4 parts per 100 parts of monomer, with theratio of nonylphenol polyethylene oxide ether sulfate to thepropoxylated, ethyoxylated propylene glycol nonionic surfactant blockpolymer from about 1:2 to about 10:1, more preferably about 1:1.

The preferred method for preparing the polymer and the resulting latexcomposition of the present invention is by the free-radical emulsionpolymerization of the monomers as initiated by any of the knownfree-radical initiators, such as the various organic and inorganicperoxides, e.g., lauryl peroxide, hydrogen peroxide, tertiary bubylhydroperoxide and the various percabonates, persulfates, perborates, andthe like. The amount of initiator used will depend upon the desiredpolymerization rate for a given amount of monomer being polymerized andthe desired molecular weight of the polymer. It has been determined thatthe concentration of initiator necessary to effectively polymerize themonomers at a commercially attractive rate is at least about 0.0073parts per 100 parts of monomer (phm) being polymerized, and preferablyfrom about 0.0073 to about 0.132 phm, and still more preferably fromabout 0.0073 to about 0.025 phm. The preferred free radical initiator istertiary butyl hydroperoxide. More preferably, a catalyst is used, suchas sodium formaldehyde sulfoxylate, to speed up the reaction of theinitiator in forming the free radical. The use of a catalyst also allowsthe reaction to be carried out at lower temperatures, for example, 32°F.

A batch emulsion free-radical polymerization process useful for thepreparation of the composition of the present invention generallyinvolves preparing an aqueous mixture of the surfactant, either thenonylphenol polyethylene oxide ether sulfate alone or in combinationwith the propoxylated, ethoxylated propylene glycol block polymer, andthe monomers being polymerized with the concurrent or subsequentaddition of at least one free-radical initiator and preferably theaddition of at least one catalyst. The initiator may be added all atonce, or stepwise. The polymerization reaction is typically carried outat ambient temperatures, usually from about 60° F. to 90° F. or as lowas 35° F. with the use of the catalyst. After the free-radicalpolymerization is completed, the composition should have a pH of fromabout 2 to about 4 and more preferably of about 3.

The stable latex composition of the present invention is particularlysuitable for use in the enhanced recovery of oil from a subterraneanformation. The latex composition is useful in increasing the viscosityof water injected into a subterranean formation so as to displace theoil.

In preparing this viscous polymer solution, the latex composition isfirst diluted with water and neutralized. The latex composition isdiluted with a sufficient amount of water to form an aqueous mixturehaving from about 1 to about 5 weight percent solids of polymer andpreferably having 2 weight percent polymer. Preferably the water used asthe diluent is fresh water. While a source of water other than freshwater may be used as the diluent, there is a potential of forming aflaky percipitate with high salt containing water. This flakypercipitate may usually be redispersed during the neutralization of themixture. This neutralization is carried out concurrent with orsubsequent to the dilution, using a caustic aqueous solution such as anammonium hydrioxide solution, sodium hydroxide solution, potassiumhydroxide solution, or any of the other known caustic solutions.Typically, this caustic solution is in a concentrated form, for example,from 0.2N to 1N and preferably 0.5N. The caustic solution is generallyprepared using fresh water. The resulting aqueous mixture has a pH fromabout 6.5 to about 11, and more preferably a pH of about 8.5. Thisneutralization and dilution may be conducted at the well site or carriedout previous to transportation thereto.

The neutralized diluted latex composition is then used to increase theviscosity of water, typically field brine, at the well site to form aviscous polymer solution of any desired weight percent solids of thepolymer. Generally, the concentration of polymer in the viscous polymersolution is dependent upon the final viscosity desired by the end user.Typically, it is desirable that the viscous polymer solution have aweight percent solids of polymer sufficient to yield a viscosity ratioof water to oil of at least about 1.0, preferably from about 1.0 toabout 10 at reservoir temperature as determined by measuring theviscosity using any of the known means, such as a Brookfield viscometer,of both the oil and the viscous polymer solution and dividing theviscosity of the solution by that of the oil. The viscosities aretypically measured using a Brookfield viscometer equipped with a Number4 spindle. Preferably, the final concentration of the polymer in theviscous polymer solution is from about 200 to about 4000 parts permillion polymer, and more preferably at about 1000 parts per millionpolymer.

The viscous polymer solution may then be injected into an oil bearingsubterranean formation by any of the known techniques. Some of thevarious enhanced oil recovery techniques in which the viscous polymersolution of the present invention may be used are polymer flooding,micellar-polymer flooding, and alkaline flooding.

In polymer flooding a preflush liquid, such as, an aqueous sodiumchloride solution (about 1% NaCl) or an aqueous orthosilicate solution,is optionally injected into the formation by any known means previous tothe injection of the viscous polymer solution of the present inventionso as to remove or precipitate out di- or polyvalent cations (Ca⁺⁺,Mg⁺⁺). This preflush liquid may be any of those known to those skilledin the art. After the viscous polymer solution of the present inventionis injected into the formation, an aqueous drive solution which maycontain some electrolytes, but is typically field brine, is theninjected into the formation so as to drive the viscous polymer solutionof the present invention and the oil before it toward a producing well.In micellar-polymer flooding a micellar slug containing a surfactant,alcohol, and water blended with a electrolyte such as, sodium chloride,or a soluble oil is injected into the formation by any known means priorto the injection of the viscous polymer solution of the presentinvention. In alkaline flooding an alkaline solution (caustic soda orsodium silicate) is injected into the formation by any known techniquein place of the preflush liquid prior to the injection of the viscouspolymer solution of the present invention.

The following examples serve to further illustrate and instruct oneskilled in the art the best mode of how to practice this invention andare not intended to be construed as limiting thereof.

EXAMPLES 1-24

The following examples demonstrate latex and polymer solutioncompositions of the present invention having varying weight percentsolids of polymer prepared from varying weight percents of the differentmonomers.

The latex compositions of all of the examples are prepared by a batchemulsion polymerization method. This involves charging a 4-neck flatbottom 1000 milliliter flask, which is provided with a paddle stirrer,reflux condenser, thermometer and a nitrogen inlet, with the desiredamount of water, surfactant, monomers and initiator. The reaction isstarted by the addition of the appropriate amount of catalyst (sodiumformaldehyde sulfoxylate) at room temperature. After about 25 minutesthe temperature of the mixture rises to about 150° F. because of theexothermic reaction. The reaction is continued for about 2 hours withthe mixture being constantly stirred and nitrogen being swept over themixture continuously.

Each of Examples 1-14 is prepared by individually charging a flask with440 grams of water, 28.3 grams of a nonylphenol polyethylene oxidesodium sulfate (Alipol Ep-115, sold by GAF Corp. 140 W. 51 St., N.Y.,N.Y., which has a number average ethylene oxide mole content of thepolyethylene oxide adduct of about 20), 8 drops of tertiary butylhydroperoxide solution (a 70% solution of the hydroperoxide in wateryielding approximately 0.12 grams) and a total of 170 grams of monomer(the amount of each specific monomer is given as a weight percent (wt.%) in Table 1 below for each example). After all of the ingredients ineach example have been charged to the flask, a solution of sodiumformaldehyde sulfoxylate (0.23 grams in 8.8 grams of water) is added tothe mixture to catalyze the reaction.

Each of the Examples 15-24 is prepared by individually charging a flaskwith 400 grams of water, 33.9 grams of the same nonylphenol polyethyleneoxide sodium sulfate as used for Examples 1-14, 9 drops of the sametertiary butyl hydroperoxide solution used for Examples 1-14 (yieldabout 0.135 grams of the hydroperoxide) and a total of 204 grams ofmonomer (the amount of each specific monomer given as a weight percentin Table 1 below for each example). After all of the ingredients in eachexample have been charged to the flask, a solution of sodiumformaldehyde sulfoxylate (0.27 grams in 8.8 grams of water) is added tothe mixture to catalyze the reaction.

The pH and viscosity for each composition of Examples 1-24 aredetermined and listed below in Table 1. The pH is measured using astandard pH meter, such as a PHM80 portable pH meter (sold byRadiometer, Copenhagen, Denmark) with the viscosity measured using aBrookfield Synchro-Lectric Viscometer equipped with a Number 1 spindleat room temperature, i.e., about 70° F.

Each of the latex compositions of Examples 1-24 are further diluted andneutralized so as to obtain a polymer aqueous solution compositionhaving a weight percent polymer concentrations of about 2 and a pH ofaround 7.5 (the actual pH for each of the Examples 1-24 is listed belowin Table 1 and was determined according to the procedure stated above).The solution compositions were neutralized using an aqueous 1.1 percentNaOH solution. The viscosities for each example are determined by theprocedure stated above, excepting a Number 4 spindle is used, and arelisted below in Table 1.

As the result listed in Table 1 demonstrate latex compositions comprisedof a surfactant and a polymer having monomer weight percentages inaccordance with the present invention possess low viscosities,particularly when the weight percentages of monomer are within thepreferred ranges. It is also shown that 2 percent neutralized polymersolution mixtures prepared from this latex compositions possess a highviscosity.

                                      TABLE 1                                     __________________________________________________________________________    Monomers           Latex       2 wt. % Neutralized                            (wt. %).sup.1      Viscosity                                                                          Total Solids                                                                         Mixture                                        Example                                                                            EA/AA/MAA                                                                             pH    (cp) (wt. %)                                                                              pH Viscosity (cp)                              __________________________________________________________________________    1    40/0/60 3.21  246  27.5   6.75                                                                             4,300                                       2    50/0/50 3.35  27.2 27.4   7.41                                                                             5,600                                       3    50/10/40                                                                              3.16  3064 28.7   7.23                                                                             5,960                                       4    50/15/35                                                                              coagulated                                                       5    50/20/30                                                                              coagulated                                                       6    55/15/30                                                                              3.10  32.2 27.0   7.18                                                                             5,400                                       7    55/20/25                                                                              3.21  54.8 26.3   7.17                                                                             4,860                                       8    55/25/20                                                                              2.80  5980 26.5   coagulated                                     9    60/15/25                                                                              3.33  12.2 26.9   7.92                                                                             3,660                                       10   60/20/20                                                                              3.25  14.8 26.7   7.03                                                                             5,060                                       11   60/25/15                                                                              3.12  12.2 26.7   7.34                                                                             3,400                                       12   60/30/10                                                                              coagulated                                                       13   65/10/25                                                                              3.51  15.2 26.7   7.68                                                                             3,400                                       14   65/25/10                                                                              3.12  8.2  26.9   11.1                                                                             3,380                                       15   50/0/50 3.37  432  32.5   -- --                                          16   55/15/30                                                                              syneresis                                                                           287  --     -- --                                          17   55/25/20                                                                              --    13   (32.5) -- --                                          18   55/35/10                                                                              coagulated                                                                          --   --     -- --                                          19   60/10/30                                                                              3.47  120.2                                                                              31.9   7.71                                                                             4,700                                       20   60/15/25                                                                              3.22  119  32.5   7.55                                                                             3,860                                       21   60/20/20                                                                              --    --   (32.5) -- --                                          22   65/10/25                                                                              3.02  59.2 32.0   7.39                                                                             3,280                                       23   65/15/20                                                                              3.26  46   32.2   -- --                                          24   65/20/15                                                                              coagulated                                                                          --   --     -- --                                          __________________________________________________________________________     .sup.1 EA = Ethylacrylate                                                     AA = Acrylic Acid                                                             MAA = Methylacrylic Acid                                                 

EXAMPLES 25-42

The following examples demonstrate the effectiveness of a nonylphenolpolyethylene oxide sulfate having a polyethylene oxide adduct with anumber average mole content of at least 20 ethylene oxide monomerresidues in comparison with other surfactants for preparing compositionsin accordance with the present invention.

The procedure for preparing both the latex composition and the 2 weightpercent aqueous polymer mixture is as described above for Example 1-24.The types of surfactants to be used are listed below in TABLE A with therespective ethylene oxide monomer mole content (EO) for each type.

                  TABLE A                                                         ______________________________________                                        Brand                                                                         Name     Description              EO                                          ______________________________________                                        Alipal:  Nonylphenol polyethylene oxide sulfate                               EP-120                            30                                          EP-115                            20                                          EP-110                             9                                          Aerosol:                                                                      A-102    Disodium-ethoxylated alcohol C.sub.10 -C.sub.12                                                        30                                                   half-ester of sulfosuccinic acid                                     A-103    Disodium-ethoxylated nonylphenol                                                                        9                                                   half-ester of sulfonsuccinic acid                                    Tensol:  Nonylphenol polyethylene oxide propyl                                         Sulfonate                                                            AP-21                             20                                          AP-10                             10                                          Tensol:  Alkyl-ethoxylated sulfopropyl-ether                                  AO-12                             12                                          AO-7                               7                                          Polystep B-22:                                                                         Ethoxylated alkyl sulfate                                                                              12                                                   ammonium salt                                                        ______________________________________                                    

The amounts of water, surfactant (including type), initiator, catalyst(sodium formaldehyde sulfoxylate) and monomers (listed by the type ofmonomer) used to prepare each example is listed below in Table B.Examples 25-33 have about 21 weight percent of polymer with Examples34-42 having about 26 weight percent of polymer.

                                      TABLE B                                     __________________________________________________________________________                       Monomers.sup.2                                             Example                                                                            Surfactant.sup.1                                                                       Water                                                                              (Grams)              Catalyst.sup.3                                                                     Initiator.sup.4                  No.  Type                                                                              (Grams)                                                                            (Grams)                                                                            EA  AA MAA            (Grams)                                                                           (Grams)                          __________________________________________________________________________    25   EP-120                                                                            22.6 480  74.8                                                                              34.0                                                                             27.2          0.18 0.09                             26   A-102                                                                             22.6 480  74.8                                                                              34.0                                                                             27.2          0.18 0.09                             27   EP-115                                                                            22.6 480  74.8                                                                              34.0                                                                             27.2          0.18 0.09                             28   A-103                                                                             22.6 480  74.8                                                                              34.0                                                                             27.2          0.18 0.09                             29   AP-20                                                                             6.8  495  74.8                                                                              34.0                                                                             27.2          0.18 0.09                             30   B-22                                                                              22.6 480  74.8                                                                              34.0                                                                             27.2          0.18 0.09                             31   AO-12                                                                             6.8  495  74.8                                                                              34.0                                                                             27.2          0.18 0.09                             32   AP-10                                                                             6.8  495  74.8                                                                              34.0                                                                             27.2          0.18 0.09                             33   AO-7                                                                              6.8  495  74.8                                                                              34.0                                                                             27.2          0.18 0.09                             34   EP-120                                                                            28.3 440  102 34 34            0.23 0.12                             35   A-102                                                                             28.3 440  102 34 34            0.23 0.12                             36   AP-20                                                                             28.3 440  102 34 34            0.23 0.12                             37   EP-115                                                                            28.3 440  102 34 34            0.23 0.12                             38   A-103                                                                             10   460  102 34 34            0.23 0.12                             39   AP-12                                                                             10   460  102 34 34            0.23 0.12                             40   AO-10                                                                             10   460  102 34 34            0.23 0.12                             41   EP-110                                                                            28.3 440  102 34 34            0.23 0.12                             42   AO-7                                                                              10   460  102 34 34            0.23 0.12                             __________________________________________________________________________     .sup.1 All of the surfactants are in a solution with about 30% activity       except for Tensol surfactants which have 100% activity. Assumed inactive      portion is water so total amount water + surfactant is about 502 grams fo     Examples 25-33 and about 470 grams for Examples 34-42.                        .sup.2 EA, AA, and MAA are same as listed TABLE 1 with the weight             percentges of monomers as EA/AA/MAA ratio for Examples 25-33 is 55/25/20      and for Examples 34-42 is 60/20/20.                                           .sup.3 Catalyst is a solution of 0.18 grams of the sulfoxylate in 8.8         grams of water for Examples 25-33 and 0.23 grams of the sulfoxylate in 8.     grams of water for Examples 34-42.                                            .sup.4 Initiator is a 70% solution of the hydroperoxide in water with 6       drops of the solution used for Examples 25-33 and 8 drops used for            Examples 34-42.                                                          

The pH and viscosity is measured for the latex composition and the 2percent polymer mixture of each respective latex composition for eachexample according to the procedures set forth about for Example 1-24with the results listed below in Table 2. As demonstrated by the resultsindicated below in Table 2 those compositions prepared from thesurfactant of the present invention (Exs. 25, 27, 34, and 37) generallyexhibited lower viscosities with the 2 percent neutralized mixturesprepared from these compositions generally possessing higher viscositiesthan compositions prepared with other surfactants.

                  TABLE 2                                                         ______________________________________                                        Ex-                                                                           am-            Total               2% Mixture                                 ple  Type      Solids         Viscosity   Viscosity                           No.  Surfactant                                                                              (wt. %)   pH   (cp)   pH   (cp)                                ______________________________________                                        25   EP-120    21.0      3.11 7.8    7.36 6,080                               26   A-102     21.0      3.36 28.4   7.66 5,960                               27   EP-115    20.7      3.28 8.8    7.80 6,900                               28   A-103     21.4      3.27 19.4   7.65 6,880                               29   AP-20     --        --   --     --   --                                  30   B-22      --        --   --     --   --                                  31   AO-12     21.0      2.52 724.0  --   --                                  32   AP-10     20.5      2.75 21.6   --   --                                  33   AO-7      --        --   --     --   --                                  34   EP-120    27.2      3.29 17.0   7.20 3,200                               35   A-102     26.3      3.70 81.2   7.89 3,820                               36   AP-20     26.7      2.88 11.6   7.21 2,720                               37   EP-115    26.7      3.25 14.8   7.03 5,060                               38   A-103     26.7      3.70 43.0   7.48 5,160                               39   AO-12     (unstable)     676.0  7.67 5,160                               40   AP-10     (syneresis)    285.0  7.69 1,040                               41   EP-110    --        --   --     --   --                                  42   AO-7      --        --   --     --   --                                  ______________________________________                                    

EXAMPLES 43-59

In the following examples the amounts of the surfactants and theinitiator (tertiary butyl hydroperoxide) are varied. The amounts ofmonomer necessary to prepare Examples 43-51 are the same as for theamounts used in Examples 25-33 above with the amounts for preparingExamples 52-59 the same as for the amounts used in Examples 34-42 above.The amounts of water, surfactant (in both grams and parts per hundredparts monomer (phm)) and initiator (tertiary butyl hydroperoxide in phm)added for each example is listed below in Table C. The amount ofcatalyst used for each example is at a 2:1 weight ratio with respect tothe amount of initiator used.

                  TABLE C                                                         ______________________________________                                        Surfactant                                                                    Example         Amount         Initiator                                                                            Water                                   No.     Type    (Grams)    (phm) (phm)  (Grams)                               ______________________________________                                        43      EP-115  22.6       5.0   0.066  480                                   44      EP-115  22.6       5.0   0.022  480                                   45      EP-115  11.3       2.5   0.066  490                                   46      EP-115  11.3       2.5   0.022  490                                   47      AP-20   12.0       7.5   0.066  490                                   48      AP-20   8.0        5.0   0.066  495                                   49      AP-20   4.0        2.5   0.066  500                                   50      AO-12   8.0        5.0   0.066  495                                   51      AO-12   12.0       7.5   0.066  490                                   52      EP-115  28.3       5.0   0.132  440                                   53      EP-115  28.3       5.0   0.066  440                                   54      EP-115  28.3       5.0   0.055  440                                   55      EP-115  14.1       2.5   0.066  455                                   56      AP-20   10.0       5.0   0.066  460                                   57      AP-10   10.0       5.0   0.066  460                                   58      AP-10   5.0        2.5   0.066  465                                   ______________________________________                                    

The pH and viscosity is measured for the latex composition and the 2percent polymer mixture (as prepared according to the above statedprocedures) of each respective latex composition for each exampleaccording to the procedures set forth above for Examples 1-24 with theresults listed below in Table 3.

                                      TABLE 3                                     __________________________________________________________________________                                     2% Neutralized                                                 Latex                                                                             Latex      Polymer Solution                             Example                                                                            Surfactant                                                                            Initiator                                                                          Solids                                                                            Viscosity  Viscosity                                    No.  (phm)                                                                             Type                                                                              (phm)                                                                              (wt %)                                                                            pH    (cps)                                                                              pH   (cps)                                   43   5.0 EP-115                                                                            0.066                                                                              20.7                                                                              3.28  8.8  7.80 6,900                                   44   5.0 EP-115                                                                            0.022                                                                              20.6                                                                              3.08  14.0 7.41 6,760                                   45   2.5 EP-115                                                                            0.066                                                                              20.4                                                                              3.03  8.8  7.47 6,760                                   46   2.5 EP-115                                                                            0.022                                                                              20.2                                                                              3.03  12.6 7.52 7,200                                   47   7.5 AP-20                                                                             0.066                                                                              --  coagulated                                              48   5.0 AP-20                                                                             0.066                                                                              --  coagulated                                              49   2.5 AP-20                                                                             0.066                                                                              --  coagulated                                              50   5.0 AO-12                                                                             0.066                                                                              --  coagulated                                              51   7.5 AO-12                                                                             0.066                                                                              26.1                                                                              3.12  2640.0                                                                             syneresis                                    52   5.0 EP-115                                                                            0.132                                                                              26.8                                                                              3.33  12.8 7.90 4,500                                   53   5.0 EP-115                                                                            0.066                                                                              26.7                                                                              3.25  14.8 6.03 5,060                                   54   5.0 EP-115                                                                            0.055                                                                              26.7                                                                              3.27  13.6 7.78 4,800                                   55   2.5 EP-115                                                                            0.066                                                                              26.1                                                                              3.11  11.0 7.36 4,000                                   56   5.0 AP-20                                                                             0.066                                                                              26.7                                                                              2.88  11.6 7.21 2,720                                   57   5.0 AP-10                                                                             0.066                                                                              26.5                                                                              2.82  285  7.69 1,040                                   58   2.5 AP-10                                                                             0.066                                                                              26.0                                                                              2.99  12.4 8.46 4,540                                   __________________________________________________________________________

EXAMPLES 59-76

The following examples demonstrate the use of the co-surfactant systemin preparing the latex composition and the 2 weight percent aqueouspolymer solution.

The procedure for preparing the latex and polymer solution compositionsand mixture is as described above for Examples 1-24. Each latex examplewas prepared by charging 400 grams (g) water, 11.6 g of a nonylphenolpolyethylene oxide ether sulfate (Alipal EP-115, as described above inTable A), 3.4 g of a propoxylated, ethoxylated propylene glycol nonionicsurfactant block polymer (the block polymers used are sold by the BASFWyandotte Company under the designation Pluronic® surfactants), 136 g ofmonomer (with the weight percent ethylacrylate/methacrylic acid being55/20/25 and 6 drops of a 70% solution of tertiary butyl hydroperoxidein water to a one-liter 4-neck reactor and initiating the reaction bythe addition of a solution of 0.18 g of sodium formaldehyde sulfoxylatein 8.8 g of water.

The examples differed by the molecular weight of the Pluronic®surfactant used, which are listed for the respective example in Table 4below.

Also listed in Table 4 are the respective solids content in weightpercent (wt.%) for each example and pH and viscosity (in centipoise(cps)) for each of the examples for the stable latex composition andaqueous polymer solution composition, which was prepared by diluting thelatex composition as described above for Examples 1-24.

                  TABLE 4                                                         ______________________________________                                               Pluronic ®    Latex     Solution                                   Example                                                                              Surfactant                                                                              Solids  Viscosity Viscosity                                  No     MW        Wt. %   pH    (cps) pH    (cps)                              ______________________________________                                        59     5,000     19.9    2.91  14.4  7.52  7,380                              60     6,600     17.5    2.86  9.4   8.36  7,200                              61     14,000    19.5    2.98  7.0   9.40  6,460                              62     4,200     19.3    2.93  20.6  7.29  7,320                              63     4,600     19.9    2,87  9.6   --    --                                 64     5,850     20.0    2,96  14.0  7.46  7,300                              65     1,100     19.7    2.99  9.2   7.51  7,680                              66     1,850     19.1    2.81  21.2  7.53  7,960                              67     1,850     19.1    2.81  21.2  11.28 8,540                              68     2,900     19.8    2.91  25.6  7.31  7,180                              69     2,800     high coagulum                                                70     3,120     19.8    2.62  17.0  7.20  7,040                              71     3,000     19.9    2.85  14.2  7.20  6,840                              74     4,500     19.6    2.95  11.0  7.14  7,840                              75     9,000     19.5    2.92  20.2  7.50  4,540                              76     4,300     20.2    2.94  13.2  7.10  5,690                              ______________________________________                                    

As seen from the above examples, latex and polymer solution compositionsprepared with the co-surfactants exhibit generally higher viscosities incomparison to those compositions and mixtures prepared with thenonylphenol polyethylene oxide ether sulfate alone. See specificallyExamples 45 and 46 above for a comparison of these Examples withcompositions having similar amounts and ratios of monomer, surfactant,and other ingredients.

While the preferred embodiments have been described and illustrated,various substitutes and modifications may be made thereto withoutdeparting from the spirit and scope of the present invention.Accordingly, the present invention has been described by way ofillustration and not limitation, and no limitations should be imposedother than as indicated.

What is claimed is:
 1. A method for recovering petroleum from asubterranean petroleum-containing formation penetrated by at least oneinjection well and by at least one spaced-apart production well, bothwells being in fluid communication with the formationcomprising:injecting a sufficient amount of an aqueous polymer solutionthrough the injection well into the formation so as to displace thepetroleum in the formation towards the production well, said aqueouspolymer solution comprising: water; at least one polymer comprising fromabout 45 to about 65 weight percent ethylacrylate monomer residue, fromabout 10 to about 45 weight percent methylacrylic acid residue, and fromabout 10 to about 30 weight percent acrylic acid monomer residue; fromabout 2 to about 10 parts per 100 part of monomer of a co-surfactantsystem comprising:(a) at least one nonylphenol polyethylene oxide ethersulfate, wherein the polyethylene oxide adduct of the nonylphenolpolyethylene oxide ether sulfate is comprised of at least about 20 molesof ethylene oxide monomer residue; and (b) at least one propoxylated,ethoxylated propylene glycol nonionic surfactant block polymer, whereinthe ratio of said ether sulfate to said block polymer is from about 1:2to about 10:1.
 2. The method of claim 1 wherein the polymer is comprisedof about 30 to about 35 percent solids.
 3. The method of claim 2 whereinthe polymer is comprised of from about 21 to about 30 percent solids. 4.The method of claim 1 wherein the polymer is comprised from about 60 toabout 65 weight percent ethylacrylate monomer residue, from about 10 toabout 15 weight percent acrylic acid monomer residue and from about 20to about 30 weight percent methylacrylic acid monomer residue.
 5. Themethod of claim 3 wherein the polymer is comprised of from about 55 toabout 65 weight percent ethylacrylate monomer residue, from about 10 toabout 25 weight percent acrylic acid monomer residue, and from about 10to about 30 weight percent methylacrylic acid monomer residue.
 6. Themethod of claim 1 wherein the co-surfactant system is present from 2 toabout 10 parts per 100 parts of monomer.
 7. The method of claim 1wherein the co-surfactant system is present from about 2 to about 4parts per 100 parts of monomer.
 8. The method of claim 2 wherein theinjection of the aqueous polymer solution is preceded by injecting apreflush liquid into the formation so as to remove or precipitate di- orpolyvalent cations.
 9. The method of claim 2 wherein the injection ofthe aqueous polymer solution is followed by the injection of an aqueousdrive solution into the formation through the injection well so as todrive the aqueous polymer solution and the petroleum toward theproducing well.
 10. The method of claim 8 wherein the preflush liquid isfollowed by the injection of at least one micellar slug composition. 11.A method for recovering petroleum from a subterraneanpetroleum-containing formation penetrated by at least one injection welland by at least one spaced-apart production well, both wells being influid communication with the formation comprising:injecting a sufficientamount of an aqueous polymer solution through the injection well intothe formation so as to displace the petroleum in the formation towardsthe product well, said aqueous polymer soluton comprising: water; atleast one polymer comprising from about 55 to about 65 weight percentethylacrylte monomer residue, from about 10 to about 30 weight percentmethylacrylic acid residue, and from about 10 to about 25 weight percentacrylic acid monomer residue; from 2 to about 10 parts per 100 parts ofmonomer of a co-surfactant system comprising:(a) at least onenonylphenol polyethylene oxide ether sulfate, wherein the polyethyleneoxide adduct of the nonylphenol polyethylene oxide ether sulfate iscomprised of at least about 20 moles of ethylene oxide monomer residue;and (b) at least one propoxylated, ethoxylated propylene glycol nonionicsurfactant block polymer, wherein the ratio of said ether sulfate tosaid block polymer is from about 1:2 to about 10:1.
 12. The method ofclaim 11 wherein the polymer is comprised of at least about 5 percentsolids.
 13. The method of claim 12 wherein the polymer is comprised offrom about 21 to about 30 percent solids.
 14. The method of claim 13wherein the concentration of the polymer in water is about 2 weightpercent and the viscosity of the solution is at least about 3280centipoise.
 15. The method of claim 11 wherein the polymer is comprisedof from about 20 to about 35 percent solids.
 16. The method of claim 1wherein the concentration of the polymer in water is about 2 weightpercent and the viscosity of the solution is at least about 3280centipoise.
 17. A method for recovering petroleum from a subterraneanpetroleum-containing formation penetrated by at least one injection welland by at least one spaced-apart production well, both wells being influid communication with the formation comprising:injecting a sufficientamount of the aqueous polymer solution at a concentration of betweenabout 200 and 4,000 parts per million polymer through the injection wellinto the formation so as to displace the petroleum in the formationtowards the production well, said aqueous polymer solution comprising:water; at least one polymer comprising from about 60 to about 65 weightpercent ethylacrylate monomer residue, from about 20 to about 30 weightpercent methylacrylic acid monomer residue, and from about 10 to about15 weight percent acrylic acid monomer residue; and from about 2 toabout 10 parts per 100 parts of monomer of a co-surfactant systemcomprising:(a) at least one nonylphenol polyethylene oxide ethersulfate, wherein the polyethylene adduct of the nonylphenol polyethyleneoxide ether sulfate is comprised of at least about 20 moles of ethyleneoxide monomer residue; and (b) at least one propoxylated, ethoxylatedpropylene glycol nonionic surfactant block polymer, wherein the ethersulfate and block polymer are provided at a ratio to each of from about1:2 to about 10:1.
 18. The method of claim 17 wherein the concentrationof the polymer in water is about 2 weight percent and viscosity of thesolution is at least about 3280 centipoise.
 19. The method of claim 17wherein the polymer comprises from about 30 to about 35 percent solids.20. The method of claim 17 wherein the injection of the polymer ispreceded by injecting a preflush liquid to remove or precipitate di- orpolyvalent cations.